The present invention relates to a method and an apparatus capable of discriminating surely and easily various kinds of real printings, including bills, coupons, stamps, tickets and other securities, from formed ones produced by an electrophotographic copier using a toner.
The problem with advanced color copiers available today is that they allow even securities, including bills and coupons, to be forged with ease. Regarding image quality, such forged securities, or copies, are comparable with real securities. Among color copiers, a dry process electrophotographic color copier is often used for the forging purpose since it is operable at high speed and low cost while implementing recording on plain papers. In light of this, there is an increasing demand for an effective measure against the illegal use of forged securities and other printings.
To identify printings, some different methods have been proposed in the past. One of them consists in sensing the density of a particular portion of a printing and determining whether or not it lies in a predetermined range. This kind of scheme is disclosed in, for example, Japanese Patent Publication No. 52-27982. Another conventional method reads a number of data patterns from a printing in a scanning direction and compares them with respective model patterns, as taught in Japanese Patent Laid-Open Publication No. 55-9284. Alternatively, a deviation of a read value from a mean value may be compared with a reference, as proposed in Japanese Patent Publication No. 61-8478.
All the conventional methods for identification need values read from reference images (e.g. bills). In practice, however, a great number of securities which need identification are circulated throughout the world. Since storing all patterns representative of such a number of securities in a memory is impracticable, the kinds of securities to be identified should be limited. Moreover, an apparatus for implementing the identification of securities is complicated and expensive since it needs optical scanning means, positioning means, means for storing reference data, comparing means, etc.